1. Chromatography
Various techniques for the separation of complex mixtures that rely on the differential affinities of substances for a gas or liquid mobile medium and for a stationary adsorbing medium through which they pass.

2. Partitioning
Separation is based on the analyte’s relative solubility between two liquid phases or a liquid and solid
Mobile Phase
Stationary Phase
Seperation is by volatility and polarity
Solvent or gas
Bonded Phase
Solid or liquid

3. Capillary GC Column.
Capillary columns are a thin fused-silica capillary.
Typically m in length and 250 µm inner diameter.
The stationary phase is coated on the inner surface.

4. Separation
The individual components are retained by the stationary phase differently.
The components separate from each other since they are running at different speeds through the column with the eluent [gas or solvent(s)].
At the end of the column they elute one at a time depending on their retention governed by their boiling point and polarity.
Separation based on polarity and temperature (GC ? Check)

5. Separation
Boiling point- lower boiling point compounds spend more time in gas phase.
Temperature of column does not have to be above boiling point. Solids have vapor pressure.
High vapor pressure liquids used as solvents (water 25 mm Hg whereas ether 520 mm Hg/25C).

6. Separation Polarity “like absorbs likes”.
Polar compounds have longer retention time on Polar columns.
Non-polar compounds have longer retention on non-polar column.
Two types of columns in GC 3800 and 3900, a silicone based column and a PEG column (wax column).

7. Stationary Phases
The most common stationary phases in gas-chromatography columns are polysiloxanes, which contain various substituent groups to change the polarity of the phase.
The nonpolar end of the spectrum is polydimethyl siloxane, which can be made more polar by increasing the percentage of phenyl groups on the polymer.
Polyethylene glycol (carbowax) is commonly used as the stationary phase for more polar analytes.

8. Separation Carrier gas flow- high flow rate decreases retention time.
High gas flow may cause poor separation since components have little time to react with stationary phase.
There is optimum gas flow for various columns. Too high a flow causes excessive back pressure.

9. Separation
Column length- longer column usually improves resolution, but increases back pressure.
Doubling length will not double resolution
(resolution increases according to square root of length).
Generally a 30 meter column gives best resolution, analysis time and head pressure

10. Separation
An effective means to increase resolution is to decrease column ID.
The efficiency of a capillary column increases (number of theoretical plates per meter) as the ID of column decrease.
Makes sharper peaks,& decreases column bleed
Decreasing ID decreases sample capacity.
Ideal (most popular) ID is 0.25 mm.

11. Some Types of Chromatography
Lid
Paper chromatography (PC),
Thin-layer chromatography (TLC),
Two experiments in MCAL demonstrate:
Liquid chromatography (LC, including high-performance liquid chromatography, or HPLC),
Gas chromatography (GC).
Paper
Solvent front
solvent

12. GC Experiment
To compare the separation of alcohols of increasing carbon number using a general purpose silicone column and a FID detector in the Varian 3800 GC.
To measured sensitivity of instrument (LOD).
Why is LOD and LOQ important in analysis and research?

13. Gas Chromatography (a review)
Chromatographic technique that can be used to separate volatile organic compounds.
A gas chromatograph consists of a flowing mobile phase, an injection port, a separation column containing the stationary phase, detector and a controller (integrator) and data collection and storage.
Organic compounds are separated due to differences in their partitioning behavior between the mobile gas phase and the stationary phase in the column.

14. Bruker Improving the Quality of our Beer – New 456-GC Off-Flavor Beer Analyzers  
Gas Chromatography (GC) is used to identify and quantify key-flavors. A number of components need to be present with a maximum and minimum concentration to guarantee the typical flavor of the beer. Other components may not exceed a concentration level to avoid an “off–flavor”.

15. Varian (Agilent) 3800 GC Gas tanks He, N2, H2, Air Autosampler
Detectors
Injectors
Oven
Computer control and data acquisition

16. Stationary Phases
The most common stationary phases in gas-chromatography columns are polysiloxanes, which contain various substituent groups to change the polarity of the phase.
The nonpolar end of the spectrum is polydimethyl siloxane, which can be made more polar by increasing the percentage of phenyl groups on the polymer.
Polyethylene glycol (carbowax) is commonly used as the stationary phase for more polar analytes.

17. Polysiloxanes
Polysiloxanes are the most common stationary phases. They are available in the greatest variety and are the most stable, robust and versatile. Standard polysiloxanes are characterized by the repeating siloxane backbone. Each silicon atom contains two functional groups. The type and amount of the groups distinguish each stationary phase and its properties

18. Polyethylene glycol
 Polyethylene glycols stationary phases are not substituted, thus the polymer is 100% of the stated material. They are less stable, less robust and have lower temperature limits than most polysiloxanes. With typical use, they exhibit shorter lifetimes and are more susceptible to damage upon over heating or exposure to oxygen.

19. Low Bleed Phases (Arlenes)
For select stationary phases, a low bleed or "ms" version is available. These stationary phases incorporate phenyl or phenyl type groups into the backbone of the siloxane polymer. These types of stationary phases are commonly called arylenes. The phenyl group strengthens and stiffens the polymer backbone which inhibits stationary phase degradation at higher temperatures. This results in lower column bleed and, in most cases, higher temperature limits.

20. Varian (Agilent) Factor Four Capillary GC Columns.
Capillary columns are a thin fused-silica capillary.
Typically m in length and 250 µm inner diameter.
The stationary phase is coated on the inner surface.

21. Capillary Columns

22. FSOT Column

23. Capillary Columns
Capillary columns provide much higher separation efficiency than packed columns but are more easily overloaded by too much sample.
You need to dilute your sample to get good symmetrical (Gaussian) peaks
Solvent peak dominates chromatogram due to normalization of peaks.

24. GC Column
Oven

25. GC 3800- one columns FID detector:
MCAL GC Columns
GC one columns FID detector:
1) CP-sil 8 50 m, 0.2mm, .33um 5% phenyl 95% dimethyl polysiloxane
GC 3900 –one column FID detector:
1) Supelco wax-10 15m x 0.32 mm, 0.5 u
Polyetyylene glycol
Polydimethylsiloxane (PDMS) belongs to a group of polymeric organosilicon compounds that are commonly referred to as silicones.[1] PDMS is the most widely used silicon-based organic polymer, and is particularly known for its unusual rheological (or flow) properties. PDMS is optically clear, and, in general, is considered to be inert, non-toxic and non-flammable. It is occasionally called dimethicone and is one of several types of silicone oil (polymerized siloxane). Its applications range from contact lenses and medical devices to elastomers; it is present, also, in shampoos (as dimethicone makes hair shiny and slippery), food (anti-foaming agent), caulking, lubricating oils, and heat-resistant tiles

26. Simple GC Computer Gas control valve Sample injector port
FID, ECD, MS Detector
Separation Column
Temperature controlled oven
Gas is He, N2 or H2

27. Sequence of GC Injection
1. A small amount of liquid (microliters) is injected through a silicon rubber septum into the heated (>200oC) GC injector that is lined with an inert glass tube.
2. The sample is immediately vaporized.
3. A pressurized, inert, carrier gas-which is continually flowing from a gas regulator through the injector and into the GC column-sweeps the gaseous sample, solvent, and analyte, onto the column.
4. Septum purge: a small ancillary flow of carrier gas bathes the underside of the injector's septum so that hot vaporized sample gases can't interact and possibly stick to the septum. This improves peak shape and reproducibility.

28. Split / Splitless Injector
Helium

29. Split / Splitless Injector

30. ECD detector
FID Detector
Injectors

31. FID Detector
Organic compounds burning in a hydrogen- oxygen flame produce ions and electrons. These charged particles created in the combustion process create a current between the detector's electrodes.
One electrode is the metallic jet itself, the other is above the jet. The detector housing is heated so that gases produced by the combustion (mainly water) do not condense in the detector before leaving the detector chimney.
The charged particles created in that combustion process create a current between the detector's electrodes. One electrode is actually the metallic jet itself, another is close by and above the jet. The gaseous products leave the detector chamber via the exhaust. The detector housing is heated so that gases produced by the combustion (mainly water) do not condense in the detector before leaving the detector chimney.

32. FID Detector
Insulator
Cathode
Anode
Air
Hydrogen
Sample plus Helium from Column

33. FID Detector

34. The ECD or Electron Capture Detector
The ECD or electron capture detector measures electron capturing compounds (usually halogenated) by creating an electrical field in which molecules exiting a GC column can be detected by the drop in current in the field

35. ECD Detector Electrode
insulator
Radioactive Beta emitter (electrons)
waste
GC column
+ electrode
- electrode
The radioactive Nickel 63 sealed inside the ECD detector emits electrons (beta particles) which collide with and ionize the make-up gas molecules (nitrogen). This reaction forms a stable cloud of free
electrons in the ECD detector cell. The ECD electronics work to maintain a constant current equal to the standing current through the electron cloud by applying a periodic pulse to the anode and cathode. The standing current value is selected by the operator; the standing current value sets the pulse rate through the ECD cell. A standing current value of 300 means that the detector electronics will maintain a constant current of 0.3 nanoamperes through the ECD cell by periodically pulsing. If the current drops below the set standing current value, the number of pulses per second increases to maintain the standing current. When electronegative compounds enter the ECD cell from the column, they immediately combine with some of the free electrons, temporarily reducing the number remaining in the electron cloud. When the electron population is decreased, the pulse rate is increased to maintain a constant current equal to the standing current. The pulse rate is converted to an analog output, which is acquired by the PeakSimple data system. Unlike other detectors which measure an increase in signal response, the ECD detector electronics measure the pulse rate needed to maintain the standing
Electron cloud
insulator

36. Seperation of Alcohols C1 to C8 on carbowax column
The area increase from left to right, although peak height doesn’t. The number of moles decrease since equal volumes were used in mixture and density similar across the alcohols. The numcer of moles decreases from C1 to C8 because the molecules are getting larger . The decrease in the number of molles is from about .025 to .006

37. GC Exp: Fid Detector
Solvent and contamination
dichlorobenzene